You could spend the entire fourth day of your week exploring just the north shore . The north shore provides access to numerous white sand beaches that have calm waters perfect for swimming in the sea and relaxing in the sand.
The first beach accessible by road will be Hawksnest, which is perfect for a long swim and a great snorkel among the elk horn coral right from the beach. Right past Hawksnest you can stop at Gibney/Oppenheimer beach which was formerly home to the famous tire swing. The beach area is still beautiful, but the palm trees here have taken a hit from Hurricane Irma. There are still some palms left and I have seen new ones sprouting up from the fallen coconuts.
If you want a short hike to a great view point, stop at Peace Hill and you will get a terrific panoramic view of the area. Continuing on North Shore Road, you will get to the small parking lot at Jumbie Bay, an intimate beach on the west end of Trunk Bay with views of the British Virgin Islands and the north shore cays. There is a reef that extends out from each end of the beach at Jumbie and is close enough to shore to make novice snorkelers feel more at ease, but it also opens to the more challenging deep-water reefs between Jumbie and Trunk Bay for the more adventuresome.
Now you could revisit Trunk and Cinnamon Bays or keep going until you reach Maho, a favorite of both locals and visitors. Maho is a great place to snorkel with turtles in the seagrass beds about 50 yards off shore. The landscape around Maho has seen considerable change since Hurricane Irma and will take some time to get back to what previous visitors might remember. By following the road a couple of miles past Maho you will end your day at the sweeping beach of beautiful Francis Bay.